A person who will go to near-extreme to extreme lengths to be in or deepen a desired relationship, weather it be romantic, platonic, familial, etc.

When someone goes to the gym and spends 90% of the time on their phones scrolling through social media

A common term in otaku fandom, a yandere is a person (usually female) romantically obsessed with someone to the point of using violent means to get them in their arms. Often seen with a sharp weapon and a psychotic grin.

A yandere is a character, usually female, who harbors powerful affections for another person to the point of either being jealous, aggressive, controlling, or downright insane and violent to the point of killing anyone(usually also female) that looks at their supposed love interest. Typically used to refer to anime/manga characters, but there are similar cases in the real world. (at least according to 2chan)

A portmanteau of two Japanese words. Yanderu, meaning to be sick. And deredere meaning an infatuation, moonstruck, head-over heals, or lovestruck.

Contrary to the popular belief that it is the opposite of tsundere, it describes an anime character who is either psychotic or violent or both, and shows affection to the main character. Became a popular moe genre after the airing of the last episode of School Days. Other yandere characters include Ryuuguu Rena from Higurashi No Naku Koro Ni series.

Anyone who is willing to do anything for their love. They sometimes refer to the love as Senpai. When a Yandere sees someone dating, flirting, or sometimes even talking there Senpai they may kill or use other means to get rid of the rival. The do it all for love.